Systems and Methods for Variable Fly Height Measurement

ABSTRACT

Various embodiments of the present invention provide systems and methods for determining fly height. For example, a system for fly height determination is disclosed that includes a head assembly disposed in relation to a storage medium, a write channel, and a read circuit. The read circuit is operable to receive information from both the head assembly and the write channel. A frequency determination circuit is included that is operable to receive a first signal from the read circuit corresponding to information received from the write channel and to provide a first fundamental frequency and a first higher order frequency based on the first signal, and the frequency determination circuit is operable to receive a second signal from the read circuit corresponding to information received from the head assembly channel and to provide a second fundamental frequency and a second higher order frequency based on the second signal. A compensation variable calculation module is included that is operable to divide the first fundamental frequency by the first higher order harmonic to yield a compensation variable. A fly height calculation module is included that is operable to divide the second fundamental frequency by the second higher order harmonic and the compensation variable to yield an indication of a distance between the head assembly and the storage medium.

BACKGROUND OF THE INVENTION

The present inventions are related to systems and methods fortransferring information to and from a storage medium, and moreparticularly to systems and methods for positioning a sensor in relationto a storage medium.

Various electronic storage medium are accessed through use of aread/write head assembly that is positioned in relation to the storagemedium. The read/write head assembly is supported by a head actuator,and is operable to read information from the storage medium and to writeinformation to the storage medium. The height between the read/writehead assembly and the storage medium is typically referred to as the flyheight. Control of the fly height is critical to proper operation of astorage system. In particular, increasing the distance between theread/write head assembly and the storage medium typically results in anincrease in inter symbol interference. Where inter symbol interferencebecomes unacceptably high, it may become impossible to credibly read theinformation originally written to the storage medium. In contrast, a flyheight that is too small can result in excess wear on the read/writehead assembly and/or a premature crash of the storage device.

In a typical storage device, fly height is set to operate in apredetermined range. During operation, the fly height is periodicallymeasured to assure that it continues to operate in the predeterminedregion. A variety of approaches for measuring fly height have beendeveloped including optical interference, spectrum analysis of a readsignal wave form, and measuring a pulse width value of the read signal.Such approaches in general provide a reasonable estimate of fly height,however, they are susceptible to various errors. Such errors requirethat the predetermined operating range of the fly height be maintainedsufficiently large to account for the various errors. This may result insetting the fly height such that inter symbol interference is too high.

Hence, for at least the aforementioned reasons, there exists a need inthe art for advanced systems and methods for positioning a sensor inrelation to a storage medium.

BRIEF SUMMARY OF THE INVENTION

The present inventions are related to systems and methods fortransferring information to and from a storage medium, and moreparticularly to systems and methods for positioning a sensor in relationto a storage medium.

Various embodiments of the present invention provide methods forcalculating relative fly height. Such methods include disposing a headassembly a fly height distance from a storage medium, writing a writepattern from a write circuit, and receiving the write pattern at theread circuit. Based on the write pattern, a compensation variable iscalculated and stored. A stored pattern is received from the storagemedium, and based at least on the stored pattern and the compensationvariable, an indication of the fly height distance is calculated. Insome instances of the aforementioned embodiments, the write pattern andthe stored pattern are periodic patterns such as 2 T, 3 T, 4 T, 5 T, 6T, . . . , or the like. A 2 T pattern includes two logic 1s followed bytwo logic 0s. Similarly, a 3 T pattern includes three logic 1s followedby three logic 0s. Other periodic patterns exhibit similar periodicity.

In some cases, calculating the compensation variable includesdetermining a fundamental frequency of a signal corresponding to thereceived write pattern, and determining a higher order harmonic of thesignal corresponding to the received write pattern. The fundamentalfrequency is divided by the higher order harmonic to create thecompensation variable. The higher order harmonic may be, but is notlimited to, a third order harmonic, a fourth order harmonic, or a sixthorder harmonic. In particular instances of the aforementionedembodiments, determining the fundamental frequency and determining thehigher order harmonic is done by performing a discrete Fouriertransform.

In various cases, calculating the indication of the fly height distanceincludes determining a fundamental frequency of a signal correspondingto the received stored pattern, and determining a higher order harmonicof the signal corresponding to the received stored pattern. Thefundamental frequency is divided by the higher order harmonic and thecompensation variable to yield the indication of the fly heightdistance. The higher order harmonic may be, but is not limited to, asecond order harmonic, a third order harmonic, a fourth order harmonic,a fifth order harmonic, a sixth order harmonic, or the like. Inparticular instances of the aforementioned embodiments, determining thefundamental frequency and determining the higher order harmonic is doneby performing a discrete Fourier transform.

In particular instances of the aforementioned embodiments, thecompensation variable accounts for one or more of temperature variationand supply voltage variation in an analog front end associated with theread circuit. In such situations, multiple compensation variables may begenerated that are specific to one or more combinations of temperatureand/or supply voltage. In various instances, the write pattern providesa fundamental frequency that corresponds to a particular disk zone ofthe storage medium. In such cases, multiple compensation variables maybe generated that are specific to particular disk zones. In someinstances, multiple compensation variables may be generated that arespecific to one or more combinations of temperature, supply voltage,and/or disk zone.

In some instances of the aforementioned embodiments, the read circuitincludes an analog front end, and the compensation variable compensatesfor temperature variation and/or supply voltage variation in the analogfront end. In such instances, calculating the compensation variableincludes calculating a first compensation variable for a firstcombination including one or more of temperature and supply voltage, andcalculating a second compensation variable for a second combinationincluding one or more of temperature and supply voltage. The methodfurther includes selecting one of the first compensation variable andthe second compensation variable based on one or more of a temperaturemeasurement and/or a supply voltage measurement. Calculating theindication of the fly height distance includes determining a fundamentalfrequency of a signal corresponding to the received stored pattern,determining a higher order harmonic of the signal corresponding to thereceived stored pattern, and dividing the fundamental frequency by thehigher order harmonic and the selected compensation variable to createthe indication of the fly height distance.

Other embodiments of the present invention provide systems fordetermining fly height. Such systems include a head assembly disposed inrelation to a storage medium, a write channel, and a read circuit. Theread circuit is operable to receive information from both the headassembly and the write channel. A frequency determination circuit isincluded that is operable to receive a first signal from the readcircuit corresponding to information received from the write channel andto provide a first fundamental frequency and a first higher orderfrequency based on the first signal, and the frequency determinationcircuit is operable to receive a second signal from the read circuitcorresponding to information received from the head assembly channel andto provide a second fundamental frequency and a second higher orderfrequency based on the second signal. A compensation variablecalculation module is included that is operable to divide the firstfundamental frequency by the first higher order harmonic to yield acompensation variable. A fly height calculation module is included thatis operable to divide the second fundamental frequency by the secondhigher order harmonic and the compensation variable to yield anindication of a distance between the head assembly and the storagemedium.

Yet other embodiments of the present invention provide storage systemsthat include a storage medium, a head assembly disposed a distance fromthe storage medium, a write circuit and a read circuit. The read circuitis operable to receive information from both the head assembly and thewrite circuit. Further, the read circuit includes at least an amplifierthat is susceptible to temperature variation and supply voltagevariation. The storage systems further include a frequency determinationmodule that is operable to receive a first signal from the read circuitcorresponding to information received from the write circuit at adefined amplifier temperature and amplifier supply voltage, and toprovide a first fundamental frequency and a first higher order frequencybased on the first signal. The frequency determination circuit is alsooperable to receive a second signal from the read circuit correspondingto information received from the head assembly channel and to provide asecond fundamental frequency and a second higher order frequency basedon the second signal. A compensation variable calculation module isincluded that is operable to divide the first fundamental frequency bythe first higher order harmonic to yield a compensation variablespecific to the defined amplifier temperature and defined amplifiersupply voltage. A temperature sensor is included to provide a measuredamplifier temperature, and a supply voltage sensor is included toprovide a measured amplifier supply voltage. A fly height calculationmodule is included that is operable to select the compensation variablebased at least in part on the measured amplifier temperature and themeasured amplifier supply voltage, and to divide the second fundamentalfrequency by the second higher order harmonic and the compensationvariable to yield an indication of the distance.

This summary provides only a general outline of some embodiments of theinvention. Many other objects, features, advantages and otherembodiments of the invention will become more fully apparent from thefollowing detailed description, the appended claims and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the various embodiments of the presentinvention may be realized by reference to the figures which aredescribed in remaining portions of the specification. In the figures,like reference numerals are used throughout several drawings to refer tosimilar components. In some instances, a sub-label consisting of a lowercase letter is associated with a reference numeral to denote one ofmultiple similar components. When reference is made to a referencenumeral without specification to an existing sub-label, it is intendedto refer to all such multiple similar components.

FIG. 1 depicts a prior art fly height measurement system;

FIG. 2 depicts a fly height measurement system including variablecompensation in accordance with one or more embodiments of the presentinvention;

FIG. 3 is a flow diagram depicting a method in accordance with someembodiments of the present invention for determining fly height;

FIG. 4 shows a fly height measurement system including variablecompensation by disk zone in accordance with one or more embodiments ofthe present invention;

FIG. 5 is a flow diagram depicting a method in accordance with someembodiments of the present invention for determining fly height usingdisk zone information;

FIG. 6 shows a fly height measurement system including variablecompensation by disk zone, temperature and voltage in accordance withone or more embodiments of the present invention; and

FIG. 7 is a flow diagram depicting a method in accordance with someembodiments of the present invention for determining fly height usingdisk zone information, temperature and voltage.

DETAILED DESCRIPTION OF THE INVENTION

The present inventions are related to systems and methods fortransferring information to and from a storage medium, and moreparticularly to systems and methods for positioning a sensor in relationto a storage medium.

Turning to FIG. 1, a prior art fly height measurement system 100 isdepicted. Fly height measurement system 100 includes a write circuit 110and a read circuit 120. Write circuit 110 includes a write channel 115that receives digital write data 105 and provides it in writable formatto a read/write head assembly 190 as is known in the art. Read circuit120 includes an analog front end 125 that receives information fromread/write head assembly 190 and provides the received data as a digitaldata stream to a data detector 195 as is known in the art. Inparticular, analog front end 125 includes an amplifier 130 that receivesthe raw analog signal from read/write head assembly 190. Amplifier 130provides an amplified output to a continuous time filter 135 thatperforms an analog low pass filter function and provides a filteredoutput to an analog to digital converter 140. Analog to digitalconverter 140 converts the analog signal to a series of digital bitsthat are provided to a data detector 195.

The output of analog to digital converter 140 is also provided to a flyheight calculation module 160 that is operable to determine whether afly height 185 is too large or too small. As shown, fly height 185 isthe distance from read/write head assembly 190 to the surface of a diskplatter 180. The relative fly height is provided as a fly height output165.

In operation, a series of logic 1s and logic 0s are originally writtento disk platter 180 such that when read they result in a sine wave atthe output of amplifier 130. The sine wave exhibits a fundamentalfrequency. Fly height calculation module 160 performs a discrete Fouriertransform that yields not only the fundamental frequency of the sinewave, but also the third harmonic of the sine wave. From this, a flyheight factor (i.e., fly height output 165) can be calculated based onthe following equation:

${{Fly}\mspace{14mu} {Height}\mspace{14mu} {Output}\mspace{14mu} 165} = {\frac{{Measured}\mspace{14mu} {Fundamental}\mspace{14mu} {Frequency}}{{Measured}\mspace{14mu} {Third}\mspace{14mu} {Harmonic}\mspace{14mu} {Frequency}}.}$

When the fly height increases, the third harmonic frequency decreasesrelative to the fundamental frequency (i.e., fly height output 165increases). When the fly height decreases, the third harmonic frequencyincreases relative to the fundamental frequency (i.e., fly height output165 decreases).

It has been determined, however, that fly height output 165 may varysubstantially over temperature, process and/or supply voltage. Hence,while the aforementioned equation provides a reasonable estimate ofrelative fly height, it can be substantially inaccurate where variationsin temperature, voltage and process exist in analog front end 125. Basedon this, it has been determined that fly height output 165 is moreaccurately represented by the following equation:

${{{Fly}\mspace{14mu} {Height}\mspace{14mu} {Output}\mspace{14mu} 165} = {\frac{{Measured}\mspace{14mu} {Fundamental}\mspace{14mu} {Frequency}}{{Measured}\mspace{14mu} {Third}\mspace{14mu} {Harmonic}\mspace{14mu} {Frequency}}*\alpha_{AFE}}},$

where α_(AFE) is a process, temperature and/or voltage dependentvariable accounting for the variation in analog front end 125. Variousembodiments of the present invention provide systems and methods thataccount for α_(AFE), and thereby provide for more accurate determinationof fly height.

Turning to FIG. 2, a fly height measurement system 200 includingvariable compensation in accordance with one or more embodiments of thepresent invention is depicted. Fly height measurement system 200includes a write circuit 210 and a read circuit 220. Write circuit 210includes a write channel 215 that receives digital write data 205 andprovides it in writable format to a read/write head assembly 290. Writecircuit 210 may be any circuit, assembly and/or processor based functioncapable of transferring information to a read/write head assembly. Basedon the disclosure provided herein, one of ordinary skill in the art willrecognize a variety of write circuits that may be used in relation todifferent embodiments of the present invention. Read circuit 220includes an analog front end 225 that receives information fromread/write head assembly 290 and provides the received data as a digitaldata stream to a data detector 295. Read circuit 220 may be any circuit,assembly and/or processor based function capable of transferringinformation from a read/write head assembly to a receiving device. Basedon the disclosure provided herein, one of ordinary skill in the art willrecognize a variety of read circuits that may be used in relation todifferent embodiments of the present invention.

Analog front end 225 may include an amplifier 230 that receives the rawanalog signal from read/write head assembly 290. Amplifier 230 providesan amplified output to a continuous time filter 235 that performs ananalog low pass filter function and provides a filtered output to ananalog to digital converter 240. Analog to digital converter 240converts the analog signal to a series of digital bits that are providedto a data detector 295. Analog front end 225 may be any circuit,assembly and/or processor based function capable of receivinginformation from a read/write head assembly and providing a digitalrepresentation thereof. Based on the disclosure provided herein, one ofordinary skill in the art will recognize a variety of analog front endsthat may be used in relation to different embodiments of the presentinvention. Further, read/write head assembly 290 may be any circuit,device and/or assembly capable of recording information to a storagemedium and for sensing information previously written to the storagemedium. Based on the disclosure provided herein, one of ordinary skillin the art will recognize a variety of read/write head assemblies thatmay be used in relation to different embodiments of the presentinvention.

A data controller circuit 245 is included that provides for directingdata from write circuit 210 to either read/write head assembly 290(i.e., standard write mode) or to read circuit 220 (i.e., loopbackmode), and from read/write head assembly 290 to read circuit 220 (i.e.,standard read mode). The output of analog to digital converter 240 isadditionally provided to a fly height calculation module 260 that isoperable to determine whether a fly height 285 is too large or toosmall. As shown, fly height 285 is the distance from read/write headassembly 290 to the surface of a disk platter 280. The relative flyheight is provided as a fly height output 265. Further, the output ofanalog to digital converter 240 is provided to a fly height calibrationmodule 250 that is operable to determine α_(AFE) for analog front end225. Fly height calibration module 250 is enabled based on a periodiccalibration enable signal 257, and the determined α_(AFE) value isupdated to a memory 255 whenever periodic calibration enable signal 257is asserted. The α_(AFE) may be retrieved from memory 255 and used byfly height calculation module 260 to calculate fly height output 265.

In operation, data controller 245 is configured in loopback mode whenperiodic calibration enable 257 is asserted so that data written viawrite circuit 210 is provided to read circuit 220. In thisconfiguration, a series of logic 1s and logic 0s are written via writecircuit 210 to read circuit. The series of logic 1s and logic 0s resultin a sine wave at the output of continuous time filter 235. It should benoted that other repetitive waveforms may be used in place of a sinewave. The sine wave exhibits a fundamental frequency. When periodiccalibration enable 257 is asserted, fly height calibration module 250performs a discrete Fourier transform on the received sine wave thatyields not only the fundamental frequency of the sine wave, but also thethird harmonic of the sine wave. From this, α_(AFE) is calculated basedon the following equation:

$\alpha_{AFE} = {\frac{{Measured}\mspace{14mu} {Fundamental}\mspace{14mu} {Frequency}\mspace{14mu} {in}\mspace{14mu} {Loopback}\mspace{14mu} {Mode}}{{Measured}\mspace{14mu} {Third}\mspace{14mu} {Harmonic}\mspace{14mu} {Frequency}\mspace{14mu} {in}\mspace{14mu} {Loopback}\mspace{14mu} {Mode}}.}$

This value of α_(AFE) is written to memory 255. In one particularembodiment of the present invention, fly height calibration module 250includes a discrete time Fourier transform circuit capable of providingthe fundamental frequency and the third harmonic frequency. These twofrequencies are provided to a processor that executes firmware/softwareinstructions that performs the mathematical manipulation of thepreceding equation. In other embodiments of the present invention, themathematical manipulation is performed in hardware.

During standard operation when periodic calibration enable 257 is notasserted, a corresponding series of logic 0s and logic 1s read from diskplatter 280 via read/write head assembly 290, and provided to readcircuit 225 by data controller 245. The output from analog to digitalconverter 240 is provided to fly height calculation module 260. Flyheight calculation module 260 performs a discrete Fourier transform thatagain yields the fundamental frequency of the sine wave and the thirdharmonic of the sine wave. From this and the value of α_(AFE) frommemory 255, a fly height factor (i.e., fly height output 265) can becalculated based on the following equation:

${{Fly}\mspace{14mu} {Height}\mspace{14mu} {Output}\mspace{14mu} 265} = {\frac{{Measured}\mspace{14mu} {Fundamental}\mspace{14mu} {Frequency}}{{Measured}\mspace{14mu} {Third}\mspace{14mu} {Harmonic}\mspace{14mu} {Frequency}}*{\alpha_{AFE}.}}$

When the fly height increases, the third harmonic frequency decreasesrelative to the fundamental frequency (i.e., fly height output 265increases). When the fly height decreases, the third harmonic frequencyincreases relative to the fundamental frequency (i.e., fly height output265 decreases). By incorporating α_(AFE) in the calculation of flyheight output 265, the variations on analog front end due totemperature, supply voltage and process can be reduced.

Turning to FIG. 3, a flow diagram 300 depicts a method in accordancewith some embodiments of the present invention for determining flyheight. Following flow diagram 300, it is determined whether acalibration process is selected (block 305). Such a calibration processmay be selected by, for example, asserting periodic calibration enable257. Where a calibration process is selected (block 305), a dataloopback is setup (block 310). Such a loopback provides for passing datawritten via a write circuit directly to the read circuit. A 6 T pattern(i.e., 111111000000 having a period of 12 T) is written via the writecircuit (block 315), and received via the read circuit (block 320). Sucha pattern yields a sine wave. Harmonic sensing is performed on the sinewave to determine the fundamental frequency of the sine wave and thethird harmonic frequency of the sine wave (block 325). In one particularembodiment of the present invention, the harmonic sensing is done usinga discrete Fourier transform that yields the fundamental frequency andthe third harmonic frequency. The fundamental frequency is divided bythe third harmonic frequency to yield α_(AFE) (block 330) that is storedto a memory (block 335).

In normal operation mode (i.e., when calibration is not selected) (block305), the system is set up to transfer information from the storagemedium to the read circuit (block 375). A 6 T pattern is read from thestorage medium (block 380), and harmonic sensing is performed on the 6 Tpattern (block 385). The harmonic sensing may be the same harmonicsensing used during the calibration phase. Thus, for example, theharmonic sensing may be done by performing a discrete Fourier transformon the sine wave generated by the 6 T pattern. This yields both thefundamental frequency of the sine wave and the third harmonic frequencyof the sine wave. The fundamental frequency is divided by the thirdharmonic frequency and the α_(AFE) value previously stored in memory(block 390). The resulting value is provided as a compensated fly heightvalue (block 395).

Turning to FIG. 4, a fly height measurement system 400 is depicted thatincludes variable compensation by disk zone in accordance with one ormore embodiments of the present invention. Fly height measurement system400 includes a write circuit 410 and a read circuit 420. Write circuit410 includes a write channel 415 that receives digital write data 405and provides it in writable format to a read/write head assembly 490.Write circuit 410 may be any circuit, assembly and/or processor basedfunction capable of transferring information to a read/write headassembly. Based on the disclosure provided herein, one of ordinary skillin the art will recognize a variety of write circuits that may be usedin relation to different embodiments of the present invention. Readcircuit 420 includes an analog front end 425 that receives informationfrom read/write head assembly 490 and provides the received data as adigital data stream to a data detector 495. Read circuit 420 may be anycircuit, assembly and/or processor based function capable oftransferring information from a read/write head assembly to a receivingdevice. Based on the disclosure provided herein, one of ordinary skillin the art will recognize a variety of read circuits that may be used inrelation to different embodiments of the present invention.

Analog front end 425 may include an amplifier 430 that receives the rawanalog signal from read/write head assembly 490. Amplifier 430 providesan amplified output to a continuous time filter 435 that performs ananalog low pass filter function and provides a filtered output to ananalog to digital converter 440. Analog to digital converter 440converts the analog signal to a series of digital bits that are providedto a data detector 495. Analog front end 425 may be any circuit,assembly and/or processor based function capable of receivinginformation from a read/write head assembly and providing a digitalrepresentation thereof. Based on the disclosure provided herein, one ofordinary skill in the art will recognize a variety of analog front endsthat may be used in relation to different embodiments of the presentinvention. Further, read/write head assembly 490 may be any circuit,device and/or assembly capable of recording information to a storagemedium and for sensing information previously written to the storagemedium. Based on the disclosure provided herein, one of ordinary skillin the art will recognize a variety of read/write head assemblies thatmay be used in relation to different embodiments of the presentinvention.

A data controller circuit 445 is included that provides for directingdata from write circuit 410 to either read/write head assembly 490(i.e., standard write mode) or to read circuit 420 (i.e., loopbackmode), and from read/write head assembly 490 to read circuit 420 (i.e.,standard read mode). The output of analog to digital converter 440 isadditionally provided to a fly height calculation module 460 that isoperable to determine whether a fly height 485 is too large or toosmall. As shown, fly height 485 is the distance from read/write headassembly 490 to the surface of a disk platter 480. The relative flyheight is provided as a fly height output 465. Further, the output ofanalog to digital converter 440 is provided to a fly height calibrationmodule 450 that is operable to determine α_(AFE) for analog front end425. Fly height calibration module 450 is enabled based on a periodiccalibration enable signal 457, and the determined α_(AFE) value isupdated to a lookup memory 455 whenever periodic calibration enablesignal 457. The α_(AFE) may be retrieved from memory 455 and used by flyheight calculation module 460 to calculate fly height output 465.

In operation, data controller 445 is configured in loopback mode whenperiodic calibration enable 457 is asserted so that data written viawrite circuit 410 is provided to read circuit 420. In thisconfiguration, a series of logic 1s and logic 0s are written via writecircuit 410 to read circuit 420. The series of logic 1s and logic 0sresult in a sine wave at the output of continuous time filter 435. Itshould be noted that other repetitive waveforms may be used in place ofa sine wave. The sine wave exhibits a fundamental frequency that differsdepending upon which of a number of disk zones 492 that the pattern isexpected to replicate. In particular, disk platter 480 is divided into anumber of radial disk zones 492 that are labeled A-G. It should be notedthat the number of disk zones is merely exemplary, and that any numberof disk zones may be employed in accordance with different embodimentsof the present invention. The fundamental frequency of a pattern writtento reflect that written to a disk zone closer to the center (e.g., diskzone G) is higher than that written to reflect that written to a diskzone closer to the outer edge (e.g., disk zone A). The particular diskzone is indicated by a disk zone input 493 that indicates which of diskzones 492 is being replicated by the data written via write circuit 410.When periodic calibration enable 457 is asserted, fly height calibrationmodule 450 performs a discrete Fourier transform on the received sinewave that yields not only the fundamental frequency of the sine wave,but also the third harmonic of the sine wave. From this, α_(AFE) iscalculated based on the following equation:

$\alpha_{AFE} = {\frac{{Measured}\mspace{14mu} {Fundamental}\mspace{14mu} {Frequency}\mspace{14mu} {in}\mspace{14mu} {Loopback}\mspace{14mu} {Mode}}{{Measured}\mspace{14mu} {Third}\mspace{14mu} {Harmonic}\mspace{14mu} {Frequency}\mspace{14mu} {in}\mspace{14mu} {Loopback}\mspace{14mu} {Mode}}.}$

This value of α_(AFE) is written to lookup memory 455 in a locationdictated by disk zone input 493. In one particular embodiment of thepresent invention, fly height calibration module 450 includes a discretetime Fourier transform circuit capable of providing the fundamentalfrequency and the third harmonic frequency. These two frequencies areprovided to a processor that executes firmware/software instructionsthat performs the mathematical manipulation of the preceding equation.In other embodiments of the present invention, the mathematicalmanipulation is performed in hardware. The process is repeated for eachof disk zones 492 with a different value of α_(AFE) being written tolookup memory 455.

During standard operation when periodic calibration enable 457 is notasserted, a corresponding series of logic 0s and logic 1s read from diskplatter 480 via read/write head assembly 490, and provided to readcircuit 425 by data controller 445. At the time the data is received,disk zone input 493 is asserted indicating which of disk zones 492 thatthe pattern was derived from. The output from analog to digitalconverter 440 is provided to fly height calculation module 460. Flyheight calculation module 460 performs a discrete Fourier transform thatagain yields the fundamental frequency of the sine wave and the thirdharmonic of the sine wave. From this and the value of α_(AFE)corresponding to the disk zone 492 identified by disk zone input 493accessed from lookup memory 455, a fly height factor (i.e., fly heightoutput 465) can be calculated based on the following equation:

${{Fly}\mspace{14mu} {Height}\mspace{14mu} {Output}\mspace{14mu} 465} = {\frac{{Measured}\mspace{14mu} {Fundamental}\mspace{14mu} {Frequency}}{{Measured}\mspace{14mu} {Third}\mspace{14mu} {Harmonic}\mspace{14mu} {Frequency}}*{\alpha_{AFE}.}}$

When the fly height increases, the third harmonic frequency decreasesrelative to the fundamental frequency (i.e., fly height output 465increases). When the fly height decreases, the third harmonic frequencyincreases relative to the fundamental frequency (i.e., fly height output465 decreases). By incorporating α_(AFE) in the calculation of flyheight output 465, the variations on analog front end due totemperature, supply voltage and process can be reduced. By using diskzones, a more accurate estimate of α_(AFE) can be generated specificallyfor a particular area from which data is generated.

Turning to FIG. 5, a flow diagram 500 depicts a method in accordancewith some embodiments of the present invention for determining flyheight using disk zone specific information. Following flow diagram 500,it is determined whether a calibration process is selected (block 505).Such a calibration process may be selected by, for example, assertingperiodic calibration enable 457. In some cases, calibration is doneduring fabrication of a storage system, during burn in of a storagemedium, or a specified or selected times during the life of the storagesystem. Where a calibration process is selected (block 505), a dataloopback is setup (block 510). Such a loopback provides for passing datawritten via a write circuit directly to the read circuit. In addition, afirst disk zone is selected for which an α_(AFE) signal will becalculated (block 512). A 6 T pattern (i.e., 111111000000 having aperiod of 12 T) is written via the write circuit (block 515), andreceived via the read circuit (block 520). The frequency of the 6 Tpattern varies depending upon the selected disk zone. Such a patternyields a sine wave. Harmonic sensing is performed on the sine wave todetermine the fundamental frequency of the sine wave and the thirdharmonic frequency of the sine wave (block 525). In one particularembodiment of the present invention, the harmonic sensing is done usinga discrete Fourier transform that yields the fundamental frequency andthe third harmonic frequency. The fundamental frequency is divided bythe third harmonic frequency to yield α_(AFE) (block 530) specific forthe selected disk zone, and the α_(AFE) value is stored to a memory atan address that corresponds to the selected disk zone (block 535).

It is then determined whether additional disk zones remain for whichα_(AFE) values are to be generated and stored to memory (block 540).Where additional disk zones remain (block 540), the next disk zone isselected (block 545) and the processes of blocks 515-540 are repeatedfor the selected disk zones. Where no additional disk zones remain(block 540), the memory has been filled with α_(AFE) values for eachrespective disk zone, and the process of calibration is consideredcomplete.

In normal operation mode (i.e., when calibration is not selected) (block505), the system is set up to transfer information from the storagemedium to the read circuit (block 575). A 6 T pattern is read from thestorage medium (block 580), and harmonic sensing is performed on the 6 Tpattern (block 585). The harmonic sensing may be the same harmonicsensing used during the calibration phase. Thus, for example, theharmonic sensing may be done by performing a discrete Fourier transformon the sine wave generated by the 6 T pattern. This yields both thefundamental frequency of the sine wave and the third harmonic frequencyof the sine wave. The disk zone from which the data is derived isdetermined (block 587), and that information is used to select theappropriate α_(AFE) value from memory. The fundamental frequency isdivided by the third harmonic frequency and the α_(AFE) value specificto the identified disk zone (block 590). The resulting value is providedas a compensated fly height value (block 595).

Turning to FIG. 6, a fly height measurement system 600 is depicted thatincludes compensation by disk zone, temperature and voltage inaccordance with one or more embodiments of the present invention. Flyheight measurement system 600 includes a write circuit 610 and a readcircuit 620. Write circuit 610 includes a write channel 615 thatreceives digital write data 605 and provides it in writable format to aread/write head assembly 690. Write circuit 610 may be any circuit,assembly and/or processor based function capable of transferringinformation to a read/write head assembly. Based on the disclosureprovided herein, one of ordinary skill in the art will recognize avariety of write circuits that may be used in relation to differentembodiments of the present invention. Read circuit 620 includes ananalog front end 625 that receives information from read/write headassembly 690 and provides the received data as a digital data stream toa data detector 695. Read circuit 620 may be any circuit, assemblyand/or processor based function capable of transferring information froma read/write head assembly to a receiving device. Based on thedisclosure provided herein, one of ordinary skill in the art willrecognize a variety of read circuits that may be used in relation todifferent embodiments of the present invention.

Analog front end 625 may include an amplifier 630 that receives the rawanalog signal from read/write head assembly 690. Amplifier 630 providesan amplified output to a continuous time filter 635 that performs ananalog low pass filter function and provides a filtered output to ananalog to digital converter 640. Analog to digital converter 640converts the analog signal to a series of digital bits that are providedto a data detector 695. Analog front end 625 may be any circuit,assembly and/or processor based function capable of receivinginformation from a read/write head assembly and providing a digitalrepresentation thereof. Based on the disclosure provided herein, one ofordinary skill in the art will recognize a variety of analog front endsthat may be used in relation to different embodiments of the presentinvention. Further, read/write head assembly 690 may be any circuit,device and/or assembly capable of recording information to a storagemedium and for sensing information previously written to the storagemedium. Based on the disclosure provided herein, one of ordinary skillin the art will recognize a variety of read/write head assemblies thatmay be used in relation to different embodiments of the presentinvention.

A data controller circuit 645 is included that provides for directingdata from write circuit 610 to either read/write head assembly 690(i.e., standard write mode) or to read circuit 620 (i.e., loopbackmode), and from read/write head assembly 690 to read circuit 620 (i.e.,standard read mode). The output of continuous time filter 635 isadditionally provided to a fly height calculation module 660 that isoperable to determine whether a fly height 685 is too large or toosmall. As shown, fly height 685 is the distance from read/write headassembly 690 to the surface of a disk platter 680. The relative flyheight is provided as a fly height output 665. Further, the output ofcontinuous time filter 635 is provided to a fly height calibrationmodule 650 that is operable to determine α_(AFE) for analog front end625. Fly height calibration module 650 is enabled based on a periodiccalibration enable signal 657, and the determined α_(AFE) value isupdated to a lookup memory 655 whenever periodic calibration enablesignal6457. The α_(AFE) value may be retrieved from memory 655 and usedby fly height calculation module 660 to calculate fly height output 665.

In operation, data controller 645 is configured in loopback mode whenperiodic calibration enable 657 is asserted so that data written viawrite circuit 610 is provided to read circuit 620. In thisconfiguration, a series of logic 1s and logic 0s are written via writecircuit 610 to read circuit 620. The series of logic 1s and logic 0sresult in a sine wave at the output of continuous time filter 635. Itshould be noted that other repetitive waveforms may be used in place ofa sine wave. The sine wave exhibits a fundamental frequency that differsdepending upon which of a number of disk zones 692 that the pattern isexpected to replicate. In particular, disk platter 680 is divided into anumber of radial disk zones 692 that are labeled A-G. It should be notedthat the number of disk zones is merely exemplary, and that any numberof disk zones may be employed in accordance with different embodimentsof the present invention. The fundamental frequency of a pattern writtento reflect that written to a disk zone closer to the center (e.g., diskzone G) is higher than that written to reflect that written to a diskzone closer to the outer edge (e.g., disk zone A). The particular diskzone is indicated by a disk zone input 693 that indicates which of diskzones 692 is being replicated by the data written via write circuit 610.When periodic calibration enable 657 is asserted, fly height calibrationmodule 650 performs a discrete Fourier transform on the received sinewave that yields not only the fundamental frequency of the sine wave,but also the third harmonic of the sine wave. From this, α_(AFE) iscalculated based on the following equation:

$\alpha_{AFE} = {\frac{{Measured}\mspace{14mu} {Fundamental}\mspace{14mu} {Frequency}\mspace{14mu} {in}\mspace{14mu} {Loopback}\mspace{14mu} {Mode}}{{Measured}\mspace{14mu} {Third}\mspace{14mu} {Harmonic}\mspace{14mu} {Frequency}\mspace{14mu} {in}\mspace{14mu} {Loopback}\mspace{14mu} {Mode}}.}$

This value is recalculated for different variations of temperature (asindicated by a temperature sensor 675) and supply voltage (as indicatedby a supply sensor 670). The calculated value of α_(AFE) is written tolookup memory 655 in a location dictated by disk zone input 693,temperature (as indicated by the output of temperature sensor 675), andsupply voltage (as indicated by the output of supply sensor 670). In oneparticular embodiment of the present invention, fly height calibrationmodule 650 includes a discrete time Fourier transform circuit capable ofproviding the fundamental frequency and the third harmonic frequency.These two frequencies are provided to a processor that executesfirmware/software instructions that performs the mathematicalmanipulation of the preceding equation. In other embodiments of thepresent invention, the mathematical manipulation is performed inhardware. The process is repeated for each of disk zones 692, andselected variations of temperature and supply voltage, with a differentvalue of α_(AFE) being written to lookup memory 655 for each of thecalculations.

During standard operation when periodic calibration enable 657 is notasserted, a corresponding series of logic 0s and logic 1s read from diskplatter 680 via read/write head assembly 690, and provided to readcircuit 625 by data controller 645. At the time the data is received,disk zone input 693 is asserted indicating which of disk zones 692 thatthe pattern was derived from. The output from continuous time filter 635is provided to fly height calculation module 660. Fly height calculationmodule 660 performs a discrete Fourier transform that again yields thefundamental frequency of the sine wave and the third harmonic of thesine wave. From this and the value of α_(AFE) corresponding to the diskzone 492 identified by disk zone input 493, temperature and supplyvoltage that is accessed from lookup memory 655, a fly height factor(i.e., fly height output 665) can be calculated based on the followingequation:

${{Fly}\mspace{14mu} {Height}\mspace{14mu} {Output}\mspace{14mu} 665} = {\frac{{Measured}\mspace{14mu} {Fundamental}\mspace{14mu} {Frequency}}{{Measured}\mspace{14mu} {Third}\mspace{14mu} {Harmonic}\mspace{14mu} {Frequency}}*{\alpha_{AFE}.}}$

When the fly height increases, the third harmonic frequency decreasesrelative to the fundamental frequency (i.e., fly height output 665increases). When the fly height decreases, the third harmonic frequencyincreases relative to the fundamental frequency (i.e., fly height output665 decreases). By incorporating α_(AFE) in the calculation of flyheight output 665, the variations on analog front end due totemperature, supply voltage and process can be reduced. By using diskzones, a more accurate estimate of α_(AFE) can be generated specificallyfor a particular area from which data is generated, and varyingtemperature and supply voltage.

Turning to FIG. 7, a flow diagram 700 depicts a method in accordancewith some embodiments of the present invention for determining flyheight using disk zone specific information. Following flow diagram 700,it is determined whether a calibration process is selected (block 705).Such a calibration process may be selected by, for example, assertingperiodic calibration enable 657. In some cases, calibration is doneduring fabrication of a storage system, during burn in of a storagemedium, or a specified or selected times during the life of the storagesystem. Where a calibration process is selected (block 705), a dataloopback is setup (block 710). Such a loopback provides for passing datawritten via a write circuit directly to the read circuit. In addition, afirst disk zone and temperature/supply voltage combination is selectedfor which an α_(AFE) signal will be calculated (block 712). A 6 Tpattern (i.e., 111111000000 having a period of 12 T) is written via thewrite circuit (block 715), and received via the read circuit (block720). The frequency of the 6 T pattern varies depending upon theselected disk zone. Such a pattern yields a sine wave. Harmonic sensingis performed on the sine wave to determine the fundamental frequency ofthe sine wave and the third harmonic frequency of the sine wave (block725). In one particular embodiment of the present invention, theharmonic sensing is done using a discrete Fourier transform that yieldsthe fundamental frequency and the third harmonic frequency. Thefundamental frequency is divided by the third harmonic frequency toyield α_(AFE) (block 730) specific for the selected disk zone, and theα_(AFE) value is stored to a memory at an address that corresponds tothe selected disk zone (block 735).

It is then determined whether additional temperature/supply voltagecombinations remain for which α_(AFE) values are to be generated for theselected disk zone (block 736). Where additional temperature/supplyvoltage combinations remain (block 736), the next temperature/supplyvoltage combination is selected (block 738) and the processes of blocks715-736 are repeated for the selected temperature/supply voltagecombination. Where no additional temperature/supply voltage combinationsremain (block 738), the memory has been filled with α_(AFE) values foreach desired temperature/supply voltage combination for the particulardisk zone.

It is then determined whether additional disk zones remain for whichα_(AFE) values are to be generated and stored to memory (block 740).Where additional disk zones remain (block 740), the next disk zone isselected (block 745) and the processes of blocks 715-740 are repeatedfor the selected disk zones. Where no additional disk zones remain(block 740), the memory has been filled with α_(AFE) values for eachrespective disk zone, temperature and supply voltage, and the process ofcalibration is considered complete.

In normal operation mode (i.e., when calibration is not selected) (block705), the system is set up to transfer information from the storagemedium to the read circuit (block 775). A 6 T pattern is read from thestorage medium (block 780), and harmonic sensing is performed on the 6 Tpattern (block 785). The harmonic sensing may be the same harmonicsensing used during the calibration phase. Thus, for example, theharmonic sensing may be done by performing a discrete Fourier transformon the sine wave generated by the 6 T pattern. This yields both thefundamental frequency of the sine wave and the third harmonic frequencyof the sine wave. The disk zone from which the data is derived isdetermined and the temperature and supply voltage are measured (block787), and that information is used to select the appropriate α_(AFE)value from memory. The fundamental frequency is divided by the thirdharmonic frequency and the α_(AFE) value specific to the identified diskzone, temperature and supply voltage (block 790). The resulting value isprovided as a compensated fly height value (block 795).

In conclusion, the invention provides novel systems, devices, methodsand arrangements for measuring fly height. While detailed descriptionsof one or more embodiments of the invention have been given above,various alternatives, modifications, and equivalents will be apparent tothose skilled in the art without varying from the spirit of theinvention. For example, the aforementioned systems and devices may bemodified for operation on higher order harmonics. Thus, for example, theapproach may include measuring the fundamental frequency and either thefourth harmonic or sixth harmonic of a 12 T pattern (i.e.,111111111111000000000000 having a period of 24 T) written in place ofthe 6 T pattern. In such a case, the following equation operates todefine α_(AFE):

$\alpha_{AFE} = {\frac{{Measured}\mspace{14mu} {Fundamental}\mspace{14mu} {Frequency}\mspace{14mu} {in}\mspace{14mu} {Loopback}\mspace{14mu} {Mode}}{\begin{matrix}{{Measured}\mspace{14mu} {Fourth}\mspace{14mu} {or}\mspace{14mu} {Sixth}} \\{{Harmonic}\mspace{14mu} {Frequency}\mspace{14mu} {in}\mspace{14mu} {Loopback}\mspace{14mu} {Mode}}\end{matrix}}.}$

Similarly, the equation for calculating the fly height output iscalculated in accordance with the following equation:

${{Fly}\mspace{14mu} {Height}\mspace{14mu} {Output}} = {\frac{{Measured}\mspace{14mu} {Fundamental}\mspace{14mu} {Frequency}}{\begin{matrix}{{Measured}\mspace{14mu} {Fourth}\mspace{14mu} {or}} \\{{Sixth}\mspace{14mu} {Harmonic}\mspace{14mu} {Frequency}}\end{matrix}}*\alpha_{AFE}}$

Based on the disclosure provided herein, one of ordinary skill in theart will recognize a variety of other measurements and calculations thatmay be done to achieve an accurate fly height in accordance withdifferent embodiments of the present invention. Therefore, the abovedescription should not be taken as limiting the scope of the invention,which is defined by the appended claims.

1. A system for determining fly height, the system comprising: a headassembly disposed in relation to a storage medium; a write channel; aread circuit, wherein the read circuit is operable to receiveinformation from both the head assembly and the write channel; afrequency determination circuit, wherein the frequency determinationcircuit is operable to receive a first signal from the read circuitcorresponding to information received from the write channel and toprovide a first fundamental frequency and a first higher order frequencybased on the first signal, and wherein the frequency determinationcircuit is operable to receive a second signal from the read circuitcorresponding to information received from the head assembly channel andto provide a second fundamental frequency and a second higher orderfrequency based on the second signal; a compensation variablecalculation module, wherein the compensation variable calculation moduleis operable to divide the first fundamental frequency by the firsthigher order harmonic to yield a compensation variable; and a fly heightcalculation module, wherein the fly height calculation module isoperable to divide the second fundamental frequency by the second higherorder harmonic and the compensation variable to yield an indication of adistance between the head assembly and the storage medium.
 2. The systemof claim 1, wherein the information received from the write channel andthe information received from the head assembly correspond to a patternselected from a group consisting of: a 6 T pattern and a 12 T pattern.3. The system of claim 1, wherein the first higher order harmonic andthe second higher order harmonic are selected from a group consistingof: a third order harmonic, a fourth order harmonic, and a sixth orderharmonic.
 4. The system of claim 1, wherein the frequency determinationcircuit implements a discrete Fourier transform.
 5. The system of claim1, wherein the system further comprises a memory, and wherein the memoryis operable to receive the compensation variable from the compensationvariable calculation module, and wherein the memory is operable toprovide the compensation variable to the fly height calculation module.6. The system of claim 5, wherein the compensation variable is a firstcompensation variable specific to a first zone of the storage medium,wherein the frequency determination circuit is operable to receive athird signal from the read circuit corresponding to information receivedfrom the write channel and to provide a third fundamental frequency anda third higher order frequency based on the third signal, wherein thethird fundamental frequency is specific to a second zone of the storagemedium, and wherein the compensation variable calculation module isoperable to divide the third fundamental frequency by the third higherorder harmonic to yield a second compensation variable specific to thesecond zone of the storage medium.
 7. The system of claim 6, wherein thefly height calculation module receives an indication that the secondinformation is derived from the second zone of the storage medium, andwherein the fly height calculation module is operable to divide thesecond fundamental frequency by the second higher order harmonic and thesecond compensation variable to yield an indication of a distancebetween the head assembly and the storage medium.
 8. A method forcalculating relative fly height, the method comprising: disposing a headassembly a fly height distance from a storage medium; writing a firstpattern from a write circuit; receiving the first pattern at the readcircuit; based at least on the first pattern, calculating a compensationvariable; storing the compensation variable; receiving a second patternfrom the storage medium; based at least on the second pattern and thecompensation variable, calculating an indication of the fly heightdistance.
 9. The method of claim 8, wherein the first pattern and thesecond pattern are 6 T patterns.
 10. The method of claim 8, whereincalculating the compensation variable includes: determining afundamental frequency of a signal corresponding to the received firstpattern; determining a higher order harmonic of the signal correspondingto the received first pattern; and dividing the fundamental frequency bythe higher order harmonic to create the compensation variable.
 11. Themethod of claim 10, wherein the higher order harmonic is selected from agroup consisting of: a third order harmonic, a fourth order harmonic,and a sixth order harmonic.
 12. The method of claim 10, whereindetermining the fundamental frequency and determining the higher orderharmonic is done by performing a discrete Fourier transform.
 13. Themethod of claim 8, wherein calculating the indication of the fly heightdistance includes: determining a fundamental frequency of a signalcorresponding to the received second pattern; determining a higher orderharmonic of the signal corresponding to the received second pattern; anddividing the fundamental frequency by the higher order harmonic and thecompensation variable to create the indication of the fly heightdistance.
 14. The method of claim 13, wherein the higher order harmonicis selected from a group consisting of: a third order harmonic, a fourthorder harmonic, and a sixth order harmonic.
 15. The method of claim 13,wherein determining the fundamental frequency and determining the higherorder harmonic is done by performing a discrete Fourier transform. 16.The method of claim 8, wherein the read circuit includes an analog frontend, and wherein the compensation variable compensates for one or morevariables of the analog front end selected from a group consisting of:temperature, supply voltage, and disk zone.
 17. The method of claim 8,wherein the read circuit includes an analog front end, and wherein thecompensation variable compensates for one or more variables of theanalog front end selected from a group consisting of: temperature andsupply voltage; and wherein calculating the compensation variableincludes calculating a first compensation variable for a firstcombination including one or more of temperature and supply voltage, andcalculating a second compensation variable for a second combinationincluding one or more of temperature and supply voltage; selecting oneof the first compensation variable and the second compensation variable;and wherein calculating the indication of the fly height distanceincludes: determining a fundamental frequency of a signal correspondingto the received second pattern; determining a higher order harmonic ofthe signal corresponding to the received second pattern; and dividingthe fundamental frequency by the higher order harmonic and the selectedcompensation variable to create the indication of the fly heightdistance.
 18. The method of claim 17, wherein selecting the one of thefirst compensation variable and the second compensation variableincludes: measuring at least one of temperature and supply voltage; andselecting one of the first compensation variable and the secondcompensation variable based on a combination of one or more of ameasured temperature and a measured supply voltage.
 19. The method ofclaim 8, wherein the storage medium includes at least a first disk zoneand a second disk zone; wherein the first pattern exhibits a fundamentalfrequency specific to the first disk zone; wherein the compensationvariable is specific to the first disk zone; and wherein the methodfurther comprises: determining that the second pattern is derived fromthe first disk zone; based at least in part on the determination thatthe second pattern is derived from the first disk zone, selecting thecompensation variable; wherein calculating the indication of the flyheight distance includes: determining a fundamental frequency of asignal corresponding to the received second pattern; determining ahigher order harmonic of the signal corresponding to the received secondpattern; and dividing the fundamental frequency by the higher orderharmonic and the selected compensation variable to create the indicationof the fly height distance.
 20. A storage system, the storage systemcomprising: a storage medium; a head assembly disposed a distance fromthe storage medium; a write circuit; a read circuit, wherein the readcircuit is operable to receive information from both the head assemblyand the write channel, wherein the read circuit includes at least anamplifier operable to amplify a received signal, and wherein theamplifier is susceptible to temperature variation and supply voltagevariation; a frequency determination module; wherein the frequencydetermination module is operable to receive a first signal from the readcircuit corresponding to information received from the write channel ata defined amplifier temperature and amplifier supply voltage, and toprovide a first fundamental frequency and a first higher order frequencybased on the first signal, and wherein the frequency determinationcircuit is operable to receive a second signal from the read circuitcorresponding to information received from the head assembly channel andto provide a second fundamental frequency and a second higher orderfrequency based on the second signal; a compensation variablecalculation module, wherein the compensation variable calculation moduleis operable to divide the first fundamental frequency by the firsthigher order harmonic to yield a compensation variable specific to thedefined amplifier temperature and defined amplifier supply voltage; atemperature sensor operable to provide a measured amplifier temperature;a supply voltage sensor operable to provide a measured amplifier supplyvoltage; and a fly height calculation module, wherein the fly heightcalculation module is operable select the compensation variable based atleast in part on the measured amplifier temperature and the measuredamplifier supply voltage, and to divide the second fundamental frequencyby the second higher order harmonic and the compensation variable toyield an indication of the distance.